Offshore floater such as FPSO, drillship is composed of topside and hull side, and the interface structure is called topside module support. In this study, practical considerations were investigated for the design of topside module supports, from the concept design stage to the final stage of structural determination, in view of design efficiency and construction productivity. The effects of welding design factors of topside module support, such as welding throat thickness, sectional welding area, and welding man-hours, were compared and analyzed closely with respect to productivity. The current status and problems regarding the application of deep or full penetration welding are discussed, and a direct-calculation method is suggested as a possible solution to these problems.